In the German patent document (Auslegeschrift) No. 25 35 019 there is described a process for the testing of rotationally symmetrical bodies which can be used in rolling bearings for material and manufacturing defects or flaws.
In this system, the body to be subjected to testing is mounted on the concavity forming a seat or recess on a cushion or layer of a liquid forming a sound-wave coupling medium, the seat constituting part of a body focusing ultrasonic acoustic energy upon the rolling body from an ultrasonic transducer. The body is surrounded by the liquid and motion is imparted to the body by a tangential jet of the liquid opening into the clearance between the seat and the body. Reflected ultrasonic waves are collected and displayed, upon separation from the applied ultrasonic signal, and the reflected signals can be displayed, e.g. on an oscilloscope or by oscillography to reveal surface and subsurface flaws resulting from material or manufacturing defects, roughness, eccentricity, etc.
It has been found that this system, while otherwise highly effective, does not provide complete satisfaction because not every point on the surface of a ball, for example, will be juxtaposed properly with the measuring unit.